Method for controlling yaw and transversal dynamics in a road vehicle

ABSTRACT

For the purpose of controlling the yaw dynamics and lateral dynamics in a road vehicle with electrically controlled four-wheel steering, in the case of which the setting of the front axle steer angle δ v  and of the rear axle steer angle δ h  is performed by means of mutually decoupled control loops, a desired value S vsoll  for the lateral force S v  to be built up at the front axle is determined in the control loop assigned to the front axle and, for this desired value S vsoll , the value of the slip angle, linked to the desired value S vsoll , is determined as desired value α vsoll  from an S v (α v ) characteristic representing the dependence of the lateral force S v , to be built up at the front axle, on the slip angle α v . In the control loop assigned to the rear axle, a desired value S hsoll  for the lateral force S h  to be built up at the rear axle is determined in a control process in accordance with a controller law of the form  
         S   hsoll     =           l   v     ·   m   ·     v   x       L     ·     [       Ψ   .     -       β   .     hsoll     +       k   1     ·     (       β   h     -     β   hsoll       )         ]                     
 
     and, for this desired value S hsoll , the value of the slip angle, linked to the desired value S hsoll , is determined as desired value α hsoll  from an S h (C h ) characteristic. These desired values α vsoll  and α hsoll  are used to determine the desired values δ vsoll  and δ hsoll  of the steer angle, taking account of an estimated value of the sideslip angle β at the centre of gravity of the vehicle, the position of the centre of gravity and measured or estimated values of the yaw velocity {dot over (Ψ)} and of the longitudinal speed v x  of the vehicle.

[0001] The invention relates to a method for controlling the yaw dynamics and lateral dynamics in a road vehicle having one steering device each for the front axle and for the rear axle, and having electrically drivable δ_(v) and δ_(h) steer angle actuators, which are assigned to said axles individually, can be driven via a controller each and which generate from desired/actual value comparisons of variables which are characteristic of the yaw-dynamic and the lateral-dynamic behaviour of the vehicle (for example of the yaw velocity {dot over (Ψ)} and of a sideslip angle β drive signals required for correcting the controlled variables, for the steer angle actuators, and having the further generically determinative features named in the preamble of patent claim 1.

[0002] In vehicles which are equipped with steer angle actuators that can be driven independently of one another for the front axle steering and the rear axle steering, it is possible in principle to obtain “extreme” vehicle movements which cannot occur in the case of a normal vehicle which can be steered only via the front wheels. For example, a sideslip of the vehicle, that is to say a movement of the same obliquely relative to the vehicle longitudinal axis, is possible without the vehicle yawing (for example by virtue of the fact that the front axle steering and the rear axle steering are set to the same steer angle with reference to the vehicle longitudinal axis). It is also possible to obtain a yawing, that is to say a rotary movement of the vehicle about its vertical axis, without the latter executing a slipping movement. The use of such vehicle movements which can be obtained only with a two-axle steering should be reserved for reasons of safety for such driving situations in which the driver consciously adopts an unaccustomed vehicle behaviour, for example manoeuvring in a very tight space, but not in the “normal” operation of the vehicle, corresponding to the statistically dominant driving situations, for which operation the driver “customarily” expects a reaction of the vehicle corresponding to the driver's wish.

[0003] It is therefore the object of the invention to specify a method of the type mentioned at the beginning which upon actuation of a steering element provided for setting a driver's wish, for example a steering wheel or joystick, leads to a vehicle reaction which is largely analogous to that of a vehicle which has only front axle steering, but yet permits improved utilization of the lateral guiding forces that can be built up by the two steer angle actuators.

[0004] This object is achieved in the case of a method of the type mentioned at the beginning by the overall combination of the features of patent claim 1 as regards the basic idea, and by means of the features of claims 2 and/or 3 in special refinements of the method according to the invention.

[0005] In this case, the type of determination of a desired value of the lateral force at the front wheels provided in accordance with claim 2 corresponds to a sideslip angle control at the front axle in the way provided in general for determining the desired value of the lateral force at the rear axle, while the type of determination of a desired value of the lateral guiding force at the front axle corresponds to a control of yaw velocity via the steer angle control loop assigned to the front axle. The approximate determination, provided in accordance with claim 4, of desired values of the slip angle of the front wheels and the rear wheels of the vehicle is sufficient in the majority of statistically significant driving situations to be able to carry out a determination of steer angle for the front and rear wheels of the vehicle that is adequate for the situation.

[0006] In the case of a control device in accordance with claim 5 which is suitable for implementing the type of control defined by the features of claim 3, a lateral acceleration sensor which directly detects the lateral acceleration active at the centre of gravity of the vehicle is particularly expedient.

[0007] Taking account of the vehicle geometry, it is also possible for this purpose, as provided in accordance with claim 6, to provide two lateral acceleration sensors whose spacing from one another measured in the longitudinal direction of the vehicle could be as large as possible.

[0008] Both owing to an ability to switch over the control device to various defined control modes, as provided in accordance with claim 7, and by means of a specific selection between different reference model variants of the vehicle which are provided in accordance with claim 8 and implemented by a computer, it is possible to set the vehicle to correspondingly different types of its response behaviour to an actuation, acting as an expression of a specific driver's wish, of a steering element, that is to say as it were the vehicle type (sports car or heavy limousine) can be selected, which corresponds to the desired driving behaviour of the vehicle. It goes without saying that the control modes explained to this extent can also be used whenever the rear axle steering is implemented by virtue of the fact that the rear wheel brakes can be driven individually to develop defined braking forces, as a result of which they can specifically influence the yaw behaviour of the vehicle via the rear wheels even without a steer angle actuator for the rear axle.

[0009] The automatic switchover of the control device to a control mode with the yaw velocity as controlled variable provided in accordance with claim 9 for the case in which the vehicle is moving in the extreme range of lateral dynamics, that is to say the lateral forces can no longer be increased by enlarging slip angles, results in the fact that the vehicle still remains capable of being effectively controlled even in the said extreme range and/or in the event of failure of the rear axle steering, and that a high measure of safety is achieved to this extent.

[0010] A significant improvement in the quality of control is achieved by means of disturbance estimators assigned to the controlled variables, preferably ones whose design model corresponds to that of the controller for the observed controlled variable, since, by contrast with a controller with an integral-action component, it is not the control error that is integrated, but the error between measurement and estimate, which can then be used to compensate disturbances.

[0011] Further details of the method according to the invention and of a device suitable for carrying it out emerge from the following description and variant configurations of a control device suitable for implementing it, with the aid of the drawing, in which:

[0012]FIG. 1 shows a schematically simplified block diagram of a device according to the invention for the control of lateral dynamics on a road vehicle with front axle steering and rear axle steering, and

[0013]FIG. 2 shows a lateral force/slip angle diagram for qualitative explanation of the functioning of the control device in accordance with FIG. 1.

[0014] In the case of the lateral dynamics control device, designated overall by 10 in FIG. 1, for a four-wheel drive road vehicle, which is denoted overall by 11 and in the case of which both the front wheels 12 and 13 and the rear wheels 14 and 16 can be steered, an electrically drivable steer angle actuator 17 or 18, respectively, being provided in each case for setting steer angles δ_(v) of the front wheels 12 and 13 and .for setting steer angles δ_(h) of the rear wheels 14 and 16, the aim is to achieve a steering behaviour which permits the vehicle to be guided by the driver in an effectively controllable fashion.

[0015] For the purpose of explanation, it may be assumed for the vehicle 11 that the front axle steer angle actuator 17 effects a “common” setting of the steer angles δ_(vl) and δ_(vr) for the two front wheels in the manner of trapeze steering, and that the same also holds for the rear axle steer angle actuator 18, such that for the purpose of a simplifying “single-track” model of the vehicle the front wheel steer angles δ_(vl) and δ_(vr) can be described by a single front axle steer angle δ_(v), and the rear wheel steer angles δ_(hl) and δ_(hr) can be described by a common “mean” rear axle angle δ_(h).

[0016] The steer angle actuators 17 and 18 can be implemented as electrohydraulic or as electromechanical actuators which can be driven by electric signals, which represent desired values δ_(vsoll) and δ_(hsoll) of the front axle steer angle δ_(v) and the rear axle steer angle δ_(h), seen in the single-track model of the vehicle 11, in order to set the relevant desired values.

[0017] These desired value signals for the front axle steer angle δ_(v) and the rear axle steer angle δ_(h) are generated by controllers 19, 21 and 22 which operate in control loops decoupled from one another, and generate drive signals characteristic of desired values for the steer angle actuators 17 and 18 from desired/actual value comparisons of variables characteristic of the lateral-dynamic behaviour of the vehicle 11, specifically the yaw angular velocity {dot over (Ψ)} at the centre of gravity 23 of the vehicle 11, the sideslip angle β_(v) in the region of the front axle 24 of the vehicle, and the sideslip angle β_(h) in the region of the rear axle 26 of the vehicle 11.

[0018] In order to convert the driver's wish for a lateral-dynamic behaviour he expects of the vehicle 11, and which the driver can input by actuating a steering element 27, for example, as illustrated, a “conventional” steering wheel or a joystick, provision is made of a reference model 28, which is implemented by an electronic computer and to which there is fed at a first input 29, the “driver's wish input”, an electric output signal, characteristic of a steer angle δ_(F), of a steering element position sensor 31 which corresponds to a steering behaviour of the vehicle 11 desired by the driver; at a second input 32, a “speed input”, the reference model 28 is fed an electric state signal which is a measure of the longitudinal speed v_(x) of the real vehicle.

[0019] The reference model 28 outputs at a first output 33 an electric output signal which is a measure of a desired value {dot over (Ψ)}_(soll) of the yaw angular velocity of the real vehicle about its vertical axis passing through the centre of gravity 23.

[0020] At a second output 34, the reference model 28 outputs an electric output signal which—in the event of cornering—is a measure of the desired value β_(vsoll) of the sideslip angle of the vehicle in the region of its front axle 24, and at a third output 36 it outputs an electric output signal which is a measure of the desired value hsoll of the sideslip angle of the real vehicle 11 at the rear axle 26 of the vehicle.

[0021] The generation of these desired values, whose input determines the reaction behaviour of the vehicle to an actuation of the steering wheel 27—setting of the steer angle δ_(F)—is expediently done so as to produce a lateral-dynamic behaviour of the vehicle 11 that is “understandable” —effectively manageable—to the driver. The reference model 28 can be designed so as to produce a “neutral” cornering behaviour to which identical slip angles α_(v) and α_(h) at the front axle 24 and the rear axle 26 correspond; however, it is also possible for the reference model 28 to be designed so as to produce a cornering behaviour of the vehicle which is easy to oversteer and approximates to that of a sports vehicle, or else to achieve an oversteering behaviour such as can be characteristic of front-wheel-drive vehicles.

[0022] Actual value signals suitable for comparison with the {dot over (Ψ)}_(soll), β_(vsoll), and β_(hsoll) value signals are generated by a vehicle model 37, which is once again implemented by an electronic computer and outputs at a first output 38 from processing-measured, operationally characteristic variables and vehicle-specific data an electric output signal which is a measure of the actual value {dot over (ω)}_(ist) of the yaw angular velocity of the vehicle 11 about its vertical axis, and outputs, furthermore, at a second output 39 an electric output signal which is a measure of the actual value β^(vist) of the sideslip angle of the front axle 24, and outputs at a third output 41 an electric output signal which is a measure of the actual value β_(hist) of the sideslip angle β_(h) at the rear axle 26 of the real vehicle 11.

[0023] Variable data suitable for generating the said actual value output signals of the vehicle model 37, that is to say ones which must be detected continuously during driving operation, and “vehicle-specific data”, that is to say ones which are permanently prescribed by the vehicle or can be detected by a single measurement and can then be regarded as constant at least for a relatively long time interval, are as follows in the case of the selected exemplary embodiment: the output signals of wheel speed sensors 42, to 424 individually assigned to the vehicle wheels 12, 13, 14 and 16, which permit accurate determination of the longitudinal speed v, of the vehicle, the output signals of an electronic or electromechanical front axle steer angle position sensor 43 assigned to the front axle steer angle actuator 17, and of a steering element position sensor 44 assigned to the rear axle steer angle actuator 18, the output signal of a yaw velocity ({dot over (Ψ)}) sensor 46 as a measure of the yaw velocity {dot over (Ψ)} about the vertical axis of the vehicle passing through the centre of gravity 23 of the same, the output signal of a lateral acceleration (a_(y)) sensor 47 as a measure of the lateral acceleration a_(y) acting at the centre of gravity 23 of the vehicle 11 perpendicular to the vehicle longitudinal direction, the x-direction, and, if appropriate, the output signal of a lateral acceleration sensor 48, expediently arranged in the vicinity of the front axle 24, and/or the output signal of a lateral acceleration (a_(yh)) sensor 49 arranged more in the vicinity of the rear axle 26 as a measure of a lateral acceleration acting in the lateral direction on the vehicle at a distance from its centre of gravity 23.

[0024] Stored in the vehicle model 37 as “vehicle-specific” data which are suitable in conjunction with the abovenamed variable data for determining the actual values {dot over (Ψ)}_(ist), β_(vist) and β_(hist) are: the wheelbase L of the vehicle and, if appropriate, the wheel track of the front and rear axles as fixed value(s), and, as variables subjected at most to slight variations, which can be corrected if required by intermittent measurement or estimation, the vehicle mass m, the distance l_(v) of the centre of gravity 23 from the front axle 24, or l_(h) of the centre of gravity 23 from the rear axle 26, the yaw moment of inertia J_(I) of the vehicle 11 about its vertical axis, and tyre characteristics, and said variables reproduce the relationship between the lateral forces S_(v) and S_(h), which can be built up by steering actuation at the front axle and the rear axle, as a function of the respective slip angles α_(v) and α_(h).

[0025] In order to explain the processing of these variables by the model computer 37, reference is made below to a simplified linearized single-track model of a road vehicle, in which the steer angles δ_(v) and δ_(h) at the front axle 24 and the rear axle 26, respectively, are given by the following relationships: $\begin{matrix} {\delta_{v} = {{- \beta} + \frac{l_{v} \cdot \overset{.}{\Psi}}{v_{x}} + \alpha_{v}}} & (1) \\ {and} & \quad \\ {\delta_{h} = {{- \beta} - \frac{l_{h} \cdot \overset{.}{\Psi}}{v_{x}} + {\alpha_{h}.}}} & (2) \end{matrix}$

[0026] In the linearized single-track model, that is to say one regarded for small values of the steer angles k and δ_(h) around 10°, selected for the purpose of explanation, the sideslip angle β at the centre of gravity of the vehicle 11 is given to a good approximation by the relationship $\begin{matrix} {\beta = {- \frac{V_{y}}{v_{x}}}} & (3) \end{matrix}$

[0027] in which v_(y) denotes the velocity component of the vehicle, produced during cornering, perpendicular to the longitudinal velocity component v_(x) of the vehicle velocity v_(F) which is yielded as the vector sum of these two velocity components.

[0028] The lateral velocity component v_(y) can be “measured”, at least approximately determined, from an integration of the lateral acceleration a_(y) acting at the centre of gravity of the vehicle, and/or be estimated from the wheel speeds, the set steer angles δ_(v) and δ_(h) and the geometrical dimensions of the vehicle.

[0029] Furthermore, the sideslip angles β_(v) and β_(h) at the front axle or the rear axle, respectively, are linked to the sideslip angle β at the centre of gravity of the vehicle by the relationships $\begin{matrix} {\beta_{v} = {\beta - \frac{J_{z} \cdot \overset{.}{\Psi}}{l_{h} \cdot m \cdot v_{x}}}} & (4) \\ {and} & \quad \\ {\beta_{h} = {\beta + {\frac{J_{z} \cdot \overset{.}{\Psi}}{l_{v} \cdot m \cdot v_{x}}.}}} & (5) \end{matrix}$

[0030] The controller 19 provided for driving the front axle steer angle actuator 17 is designed as a yaw velocity controller which uses a controller law in the form of $\begin{matrix} {S_{vsoll} = {\frac{l_{h} \cdot m \cdot a_{y}}{L} + {\frac{J_{z}}{L} \cdot \left\lbrack {{\overset{¨}{\Psi}}_{soll} - {k \cdot \left( {\overset{.}{\Psi} - {\overset{.}{\Psi}}_{soll}} \right)}} \right\rbrack}}} & (6) \end{matrix}$

[0031] to determine a desired value S_(vsoll) of the lateral force which is a function S(α_(v)) of the slip angle α_(v) at the front axle.

[0032] Corresponding to this desired value S_(vsoll) which is determined by the yaw velocity control—and by the relationship $\begin{matrix} {S_{vsoll} = {\frac{l_{h} \cdot m \cdot a_{y}}{L} + \frac{J_{z} \cdot {\overset{¨}{\Psi}}_{soll}}{L}}} & \left( 6^{\prime} \right) \end{matrix}$

[0033] in the event of a vanishing system deviation e(e={umlaut over (Ψ)}−{umlaut over (Ψ)}=0)—is the requirement, holding for stable cornering of the vehicle and expressed in general by the relationship

J _(s) ·{umlaut over (Ψ)}=S _(v) ·l _(v) −l _(b) ·S _(h)  (7),

[0034] for balancing the moments about the vertical axis of the vehicle 11 when the lateral force S_(h) occurring at the rear axle 26 of the vehicle 11 is eliminated in this relationship (7) in accordance with the relationship

m·a _(y) =S _(v) +S _(h)  (8).

[0035] Because of the dependence, reproduced qualitatively by the diagram of FIG. 2, of the lateral forces, which can be determined, mathematically as it were, in accordance with the relationship (6′), on the slip angles α to be set by the steering actuation, in accordance with the relationship $\begin{matrix} {\delta_{vsoll} = {{- \beta} + \frac{l_{v} \cdot \overset{.}{\Psi}}{v_{x}} + {\alpha_{vsoll}\quad.}}} & \left( 1^{\prime} \right) \end{matrix}$

[0036] there is linked to each by the {dot over (Ψ)} control in accordance with the relationships (6) and (6′), respectively, a desired value α_(vsoll) of the slip angle which is to be used in accordance with the relationship (1) in the determination of the desired value δ_(vsoll) for the manipulated variable δ_(v) as desired value δ_(vsoll) of the slip angle α_(v). The dependence of the lateral force S on the slip angle α is either stored in tabular form in the {dot over (Ψ)} controller 19, which is implemented for its part as a computer and determines the desired value δ_(vsoll) for the front axle steer angle δ_(v) in accordance with the relationship (1′), or implemented by a control algorithm which can be evaluated by the computer. In the case of the exemplary embodiment selected for explanation, the desired value α_(soll) of the slip angle is determined for the purpose of a linear approximation in accordance with a relationship of the form $\begin{matrix} {{\alpha_{vsoll} = \frac{S_{vsoll}}{C_{v}}},} & (9) \end{matrix}$

[0037] in which C_(v) denotes a slip stiffness characteristic of the tyre. Values of this slip stiffness can be taken from manufacturers' data or estimated or determined by suitable experiments and/or adaptive measurement methods. The approximation in accordance with the relationship (9) constitutes a sufficiently accurate approximation, at least for small slip angles (up to 10°) as may be gathered directly from the S(α) characteristic curve 51 of the diagram.

[0038] The {umlaut over (Ψ)}_(soll) value required for the evaluation of the relationship (6) or (6′) by the {umlaut over (Ψ)} controller 19 is generated by the reference model 12—by differentiating the {dot over (Ψ)}_(soll) output signal with respect to time—and is fed directly to the controller 19, as illustrated schematically by a {dot over (Ψ)}_(soll) signal path 53.

[0039] The system deviation e is determined at the {dot over (Ψ)} reference point 52 as the difference between the {dot over (Ψ)}_(ist) value signal output by the real vehicle model 37 and the {dot over (Ψ)}_(soll) value signal output by the reference model 28, and processed in the controller in accordance with the relationship (6) with the aid of a controller gain k, freely selectable in principle, of the {dot over (Ψ)} controller 19.

[0040] The inputs, further required by the {dot over (Ψ)} controller, of the variables l_(h)·m·a_(y)/L, the ratio J_(z)/L, the sideslip angle β at the centre of gravity of the vehicle and of the variable l_(v)·{dot over (Ψ)}/v_(x) are generated by the real vehicle model 37 and fed “directly” to the controller 19. The signal paths required for this purpose are represented only by a single signal path arrow 54 in FIG. 1, for the sake of simplicity.

[0041] The controller 22 provided for driving the rear axle steer angle actuator 18 is designed as a sideslip angle (β_(h)) controller, which uses a controller law of the form $\begin{matrix} {S_{hsoll} = {\frac{l_{v} \cdot m \cdot v_{x}}{L} \cdot \left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{hsoll} + {k_{2}\left( {\beta_{hist} - \beta_{hsoll}} \right)}} \right\rbrack}} & (10) \end{matrix}$

[0042] to determine a desired value for the lateral force S(α_(h)) to be built up at the rear axle 26 of the vehicle 11 by actuating the steering. This desired value that can be determined by the β_(h) control is given in the case of a vanishing system deviation (β_(hist)−β_(hsoll) =0) by the relationship $\begin{matrix} {S_{hsoll} = {{\frac{l_{v} \cdot m \cdot v_{x}}{L}\left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{hsoll}} \right\rbrack}.}} & \left( 10^{\prime} \right) \end{matrix}$

[0043] The starting point for designing the controller is the plausible assumption that the temporal change β_(h) in the sideslip angle at the rear axle 26 of the vehicle 11 is proportional to the difference between the sideslip angle actual value β_(hist) and the desired value β_(hsoll).

[0044] By being differentiated with respect to time, the relationship (5) for the sideslip angle β_(h) at the rear axle of the vehicle yields the relationship $\begin{matrix} {{{\overset{.}{\beta}}_{h} = {\overset{.}{\beta} + \frac{J_{z} \cdot \overset{¨}{\Psi}}{l_{v} \cdot m \cdot v_{x}}}},} & \left( 5^{\prime} \right) \end{matrix}$

[0045] which, taking account of the relationship (3), assumes the following form on the assumption that the longitudinal speed component v_(x) of the vehicle can be regarded as constant: $\begin{matrix} {{\overset{.}{\beta}}_{h} = {{- \frac{{\overset{.}{v}}_{y}}{v_{x}}} + {\frac{J_{z} \cdot \overset{¨}{\Psi}}{l_{v} \cdot m \cdot v_{x}}.}}} & \left( 5^{''} \right) \end{matrix}$

[0046] It follows directly from the requirement for balancing the lateral forces at the vehicle during cornering, written in the form

mv _(y) =S _(v) +S _(h) −m·v _(x)·{dot over (Ψ)}  (11)

[0047] that $\begin{matrix} {{\overset{.}{v}}_{y} = {\frac{S_{v} + S_{h}}{m} - {v_{x} \cdot {\overset{.}{\Psi}\quad.}}}} & \left( 11^{\prime} \right) \end{matrix}$

[0048] Substituting the relationship (11′) in the relationship (5″) yields the relationship $\begin{matrix} {{\overset{.}{\beta}}_{h} = {{- \frac{S_{v} + S_{h}}{m \cdot v_{x}}} + \overset{.}{\Psi} + {\frac{J_{z} \cdot \overset{.}{\Psi}}{l_{v} \cdot m \cdot v_{x}}.}}} & (12) \end{matrix}$

[0049] If the front axle lateral force S_(v) is eliminated from this relationship (12) with the aid of the relationship (7) expressing the requirement for balancing the moments in the case of the vehicle, the following relationship is yielded for the temporal change β_(h) in the sideslip angle at the rear axle 26 $\begin{matrix} {{{\overset{.}{\beta}}_{h} = {{\overset{.}{\Psi} - \frac{S_{h} \cdot l_{v}}{m \cdot v_{x} \cdot l_{v}} - \frac{l_{h} \cdot S_{h}}{l_{v} \cdot m \cdot v_{x}}} = {\overset{.}{\Psi} - \frac{L \cdot S_{h}}{m \cdot v_{x} \cdot l_{v}}}}},} & (13) \end{matrix}$

[0050] from which the following relationship follows directly for the lateral force S_(h)(α_(h)) at the rear axle $\begin{matrix} {{{S_{h}(\alpha)} = {\frac{l_{v} \cdot m \cdot v_{x}}{L} \cdot \left( {\overset{.}{\Psi} - {\overset{.}{\beta}}_{h}} \right)}},} & \left( 10^{\prime\prime} \right) \end{matrix}$

[0051] which with the desired value β_(hsoll) output for the sideslip angle control at the rear axle of the reference model corresponds to the relationship (10′)

[0052] The β_(hsoll) input required by the βh controller 22 for evaluating the relationship (10) or the relationship (10′) is generated by the reference model 28 and fed “directly” to the controller 22, as illustrated schematically by the β_(hsoll) signal path 56. The system deviation e_(h)(e_(h)=β_(hist)−β_(hsoll)) processed “multiplicatively” by the β_(h) controller 22 with the aid of the controller gain k₁, which is freely selectable in principle, is determined at the β_(h) reference point 57.

[0053] The inputs, further required by the β_(h) controller 22, for the variable l_(v)·m·v_(x)/L and for the actual value {dot over (Ψ)}_(ist) of the yaw angular velocity are generated by the real vehicle model 37 and fed “directly” to the β_(h) controller 22, as illustrated by the relevant signal paths 58 and 59.

[0054] The determination of the desired value α_(hsoll) of the slip angle α_(h) at the rear axle 26 from the desired value S_(hsoll), obtained by the sideslip angle control at the rear axle, of the lateral force at the rear axle 26 is performed in a way similar to that with reference to the {dot over (Ψ)} controller 19.

[0055] The determination of the desired value δ_(hsoll) for the rear axle steer angle to be set, that is to say the formation of the actuating signal for this angle, is performed in accordance with the relationship $\begin{matrix} {{\delta_{hsoll} = {{- \beta} - \frac{l_{h} \cdot \overset{.}{\Psi}}{v_{x}} + \alpha_{hsoll}}}\quad,} & \left( 2^{\prime} \right) \end{matrix}$

[0056] the inputs, still additionally required for this purpose, for the sideslip angle β at the centre of gravity 23 of the vehicle as well as for the variable l_(h)·Ψ_(ist)/v_(x) being generated by the real vehicle model 37 and fed to the controller 22 via signal paths which are represented only by a single signal arrow 60, for the sake of simplicity of illustration.

[0057] It is clear from the outlined type of the {dot over (Ψ)} control and the β_(h) control that the two control loops are decoupled “physically”, and this particularly benefits the robustness of the control.

[0058] In the case of the lateral dynamics control device 10, there is also provided as an alternative to driving the front axle steer angle actuator 17 with the aid of δ_(vsoll) output signals of the {dot over (Ψ)} controller 19 a drive of the front axle steer angle actuator 17 with the aid of δ_(vsoll) output signals of the further controller 21, as illustrated diagrammatically by a selector switch 61.

[0059] In functional analogy with the β_(h) controller 22 provided for driving the rear axle steer angle actuator 18, this further controller 21 is designed as a sideslip angle (β_(v)) controller which, in accordance with a controller law of the form $\begin{matrix} {{S_{vsoll} = {\frac{l_{h} \cdot m \cdot v_{x}}{L} \cdot \left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{vsoll} + {k_{2} \cdot \left( {\beta_{v} - \beta_{vsoll}} \right)}} \right\rbrack}},} & (14) \end{matrix}$

[0060] determines desired values for the lateral force S(α_(v)) to be built up at the front axle 24 of the vehicle 11 by actuating the steering.

[0061] The β_(vsoll) input required by the β_(v) controller 21 is generated by the reference model 28 and fed “directly” to the β_(v) controller 21, as illustrated diagrammatically by the β_(vsoll) signal path 62. The system deviation e_(v)(e_(v)=β_(vist)−β_(vsoll)) processed by the β_(v) controller 21 with the aid of the once again freely selectable controller gain k₂ is determined at the β_(v) reference point 63.

[0062] The inputs, further required by the β_(v) controller 21, for the variable l_(h)·m·v_(x)/L and for the actual value {dot over (Ψ)}_(ist) of the yaw angular velocity are generated by the real vehicle model 37 and fed “directly” to the β_(v) controller, as illustrated by the relevant signal paths 64 and 59′.

[0063] The determination of desired values α_(vsoll) of the slip angle α_(v) at the front axle 24 from the desired value S_(vsoll) of the lateral force obtained by the sideslip angle control at the front axle is performed as explained with the aid of the description of the {dot over (Ψ)} controller 19, similarly for the determination of the desired value δ_(vsoll) for the front axle steer angle δ_(v) to be set.

[0064] The {dot over (Ψ)} controller 19 and the β_(v) controller 21 are designed such that the reaction behaviour of the vehicle 11 in that operating mode of the lateral dynamics control device 10 in which the setting of the front axle steer angle δ_(v) is performed by means of the {dot over (Ψ)} controller 19, differs significantly from that reaction behaviour of the vehicle when the control device 10 operates in that operating mode in which the setting of the front axle steer angle δ_(v) is performed by means of the β_(v) controller 21. The vehicle 11 can therefore be set as a result of two desired modes of reaction by switching over the selector switch 61, for example to “sports”, that is to say moderately oversteering, and to neutral cornering behaviour.

[0065] Further modes of reaction—“vehicle types”— can be realized by virtue of the fact that the reference model 28 can be set selectively to various defined types of generation of its desired value output signals.

[0066] In order to improve the quality of the control, provision is made of disturbance estimators which are individually assigned to the controlled variables and whose purpose is to detect disturbances such as side wind, roadway slope and/or different adhesion coefficients at the two sides of the vehicle (μ-split ratios), and to take these into account during control for the purpose of disturbance compensation. Moreover, the disturbance estimators are also intended to compensate model errors resulting from the fact that the vehicle model can take account of reality only approximately. In accordance with the outlined decoupling of the control loops assigned to the front wheels 12 and 13, on the one hand, and to the rear wheels 14 and 16, on the other hand, for the sake of simplifying the illustration only one disturbance estimator 66 for the front axle control loop and one disturbance estimator 67 for the β_(h) control loop are illustrated. The disturbance estimators 66 and 67 are designed, in general, as models of the controlled system which are implemented by electronic computers and receive the same inputs, specifically the desired value output signals of the assigned controllers 19 and 22, as the assigned controlled systems, and generate therefrom outputs corresponding to the controlled variables {dot over (Ψ)} and β_(h), and generate from the comparison of their relevant outputs with the corresponding outputs of the vehicle model 37 of the real vehicle estimated values Â_(v,h) for the respective disturbance, their feedback to the controller 19 or 22 rendering it possible for the system deviation to be caused to vanish.

[0067] A suitable design of such a disturbance estimator which can be extended to the further control loops may be explained in more detail on the example of the β_(h) control loop:

[0068] The starting point for designing the estimator 67 is the relationship $\begin{matrix} {{\overset{.}{\beta}}_{h} = {\overset{.}{\Psi} - \frac{L \cdot c_{h} \cdot \alpha_{h}}{m \cdot v_{x} \cdot l_{v}} + \Delta_{h}}} & \left( 13^{\prime} \right) \end{matrix}$

[0069] for the temporal change in the controlled variable β_(h), which results when the lateral force S_(h) in accordance with the relationship (9) is replaced in the relationship (13), which also corresponds to the design model of the controller 22, by the relationship

S_(h)=c_(h)·α_(h)  (9′)

[0070] and Δ_(h) is used to denote a deviation from the model relationship (13) which is determined, inter alia, by the linearization of the lateral force S_(h).

[0071] It is assumed for this disturbance Δ_(h) with reference to the estimator model that it is quasi-constant in time, that is to say that it holds that:

{dot over (Δ)}_(h)=0  (13″)

[0072] Starting from this model, the disturbance estimator 67 is designed in accordance with the relationships $\begin{matrix} {{\overset{\overset{.}{\hat{}}}{\beta}}_{h} = {{\hat{\Delta}}_{h} + \overset{.}{\Psi} - \frac{L \cdot c_{h} \cdot \alpha_{h}}{m \cdot v_{x} \cdot l_{v}} + {k \cdot \left( {\beta_{hist} - {\hat{\beta}}_{h}} \right)}}} & (14) \end{matrix}$

[0073] and

{circumflex over ({dot over (Δ)})}_(h)=k′·(β_(hist)−{circumflex over (β)}_(h))  (15).

[0074] Here, in the relationship (14) k denotes a gain with which the difference β_(hist)−{circumflex over (β)}_(h) is fed back into the estimator model represented by the relationship (13′), and k′ denotes the gain with which the said difference is fed back to the model of disturbance represented by the relationship (13″).

[0075] The gains k and k′ can be determined by pole prescription using the known root locus method. The actual value β_(hist) is available as output of the real vehicle.

[0076] Numerical integration of the relationships (14) and (15) using known methods, for example the Euler method or the Runge-Kutta method, yields the sought disturbance Δĥ_(h), which is taken into account for the purpose of balancing disturbances when forming the desired value of the rear axle steer angle δ_(hsoll) in accordance with the relationship $\begin{matrix} {\delta_{hsoll} = {{- \beta} - \frac{l_{h} \cdot \overset{.}{\Psi}}{v_{x}} + \alpha_{hsoll} - {{\hat{\Delta}}_{h} \cdot {\frac{m \cdot l_{v} \cdot v_{x}}{L \cdot c_{h}}.}}}} & (16) \end{matrix}$ 

1. Method for controlling the yaw dynamics and lateral dynamics in a road vehicle having one steering device each for the front axle and for the rear axle, and having electrically drivable 8 v and δ_(h) steer angle actuators (17 and 18), which are assigned to said axles individually, can be driven via a controller each and which generate from desired/actual value comparisons of variables which are characteristic of the yaw-dynamic and the lateral-dynamic behaviour of the vehicle, for example of the yaw velocity {dot over (Ψ)} and of a sideslip angle β, drive signals, required for correcting the controlled variables, for the steer angle actuators, the control loops provided for setting the steer angles δ_(v) and δ_(h) being decoupled from one another, and the desired value prescription signals, required for the two control loops, for the control parameters being generated by means of a reference model (28), implemented by an electronic computer, from a processing of at least one output signal, representing the driver's wish, from a steering element position sensor (31), and of a sensor output signal characteristic of the operating state of the vehicle, for example a speed sensor, characterized by the following features: (a) a desired value S_(vsoll) for the lateral force S_(v) to be built up at the front axle is determined in a control process in the control loop assigned to the front axle; (b) for this desired value S_(vsoll), the value of the slip angle, linked to the desired value S_(vsoll), is determined as desired value α_(vsoll) from an S_(v)(α_(v)) characteristic representing the dependence of the lateral force S_(v), to be built up at the front axle, on the slip angle α_(v) at the front axle, and the absolute value δ_(vsoll) of the front axle steer angle, which is set by means of the front axle steer angle actuator, is determined in accordance with the relationship $\delta_{vsoll} = {{- \beta} + \frac{l_{v} \cdot \overset{.}{\Psi}}{v_{x}} + \alpha_{{vsoll};}}$

(c) a desired value S_(hsoll) for the lateral force S_(h) to be built up at the rear axle is determined in a control process in accordance with a controller law of the form $S_{hsoll} = {\frac{l_{v} \cdot m \cdot v_{x}}{L} \cdot \left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{hsoll} + {k_{1} \cdot \left( {\beta_{h} - \beta_{hsoll}} \right)}} \right\rbrack}$

 in the control loop assigned to the rear axle; and (d) for this desired value S_(hsoll) of the rear axle lateral force, the value of the slip angle, linked to the desired value S_(hsoll), is determined as desired value α_(hsoll) from an S_(h)(α_(h)) characteristic, and the absolute value δ_(hsoll) of the rear axle steer angle which is set by means of the rear axle steer angle actuator is determined in accordance with the relationship $\delta_{hsoll} = {{- \beta} - \frac{l_{h} \cdot \overset{.}{\Psi}}{v_{x}} + {\alpha_{hsoll}.}}$


2. Method according to claim 1, characterized in that the desired value S_(vsoll) of the lateral force to be built up at the front axle is determined in a control process in accordance with a controller law of the form $S_{vsoll} = {\frac{l_{h} \cdot m \cdot v_{x}}{L} \cdot {\left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{vsoll} + {k_{2} \cdot \left( {\beta_{v} - \beta_{vsoll}} \right)}} \right\rbrack.}}$


3. Method according to claim 1, characterized in that the desired value S_(vsoll) of the lateral force to be built up at the front axle is determined in a control process in accordance with a controller law of the form $S_{vsoll} = {\frac{l_{h} \cdot m \cdot a_{\gamma}}{L} + {\frac{J_{g}}{L} \cdot {\left\lbrack {{\overset{¨}{\Psi}}_{soll} - {k_{3} \cdot \left( {\overset{.}{\Psi} - {\overset{.}{\Psi}}_{soll}} \right)}} \right\rbrack.}}}$


4. Method according to one of claims 1 to 3, characterized in that the desired value α_(vsoll) of the slip angle α_(v) at the front axle and/or the desired value α_(hsoll) of the slip angle ah at the real axle is obtained from a linear relationship of the form $\delta_{{vsoll},{hsoll}} = \frac{S_{{vsoll},{hsoll}}}{C_{v,h}}$

in which C_(v,h) respectively denote estimated values, or values determined by measurement, of slip stiffnesses of the front wheel tyres (index “v”) or of the rear wheel tyres (index “h”), respectively.
 5. Device for carrying out the method according to one of claims 1 to 4 on a road vehicle (11) having one steering device each for the front axle (24) and for the rear axle (26), and having electrically drivable steer angle actuators (17 and 18), assigned to said axles individually, for two mutually decoupled control loops by means of which the front axle steer angle δ_(v) and the rear axle steer angle δ_(h) can be set, characterized in that there is provided in each case at least one lateral acceleration sensor (47) by means of which a lateral acceleration a_(y) occurring on the vehicle (11) can be detected at a defined point of the vehicle, preferably at its centre of gravity.
 6. Device according to claim 5, characterized in that two lateral acceleration sensors (48 and 49) are provided which, seen in the direction of the vehicle longitudinal axis, are arranged at a spacing from one another, it being preferred for one lateral acceleration sensor (48) to be arranged in the region of the front axle (24) and for the other lateral acceleration sensor (49) to be arranged in the region of the rear axle (26) of the vehicle (11).
 7. Device, in particular according to claim 5 or claim 6, characterized by its ability to switch over between the control mode in which the desired value S_(vsoll) of the lateral force at the front axle is determined in accordance with the controller law ${S_{vsoll} = {\frac{l_{h} \cdot m \cdot v_{x}}{L} \cdot \left\lbrack {\overset{.}{\Psi} - {\overset{.}{\beta}}_{vsoll} + {k_{2} \cdot \left( {\beta_{v} - \beta_{vsoll}} \right)}} \right\rbrack}},$

and the control mode in which the desired value of the lateral force at the front axle is determined in accordance with the controller law $S_{vsoll} = {\frac{l_{h} \cdot m \cdot a_{y}}{L} + {\frac{J_{g}}{L} \cdot {\left\lbrack {{\overset{¨}{\Psi}}_{soll} - {k_{3} \cdot \left( {\overset{.}{\Psi} - {\overset{.}{\Psi}}_{soll}} \right)}} \right\rbrack.}}}$


8. Device, in particular according to one of claims 5 to 7, characterized in that a reference model (28) provided for generating the prescribed desired values for the front axle and rear axle steer angles δ_(v) and δ_(h) to be set can be set to various defined algorithms for generating these desired values.
 9. Device according to claim 7 or 8, characterized in that an automatic switchover is performed from the control mode in which the desired value S_(vsoll) of the lateral force at the front axle is determined as a function of the system deviation (β_(v)−β_(vsoll)) of the sideslip angle in the region of the front axle, into the control mode in which the desired value S_(vsoll) of the lateral force at the front axle is determined as a function of the system deviation ({dot over (Ψ)}−Ψ_(soll)) of the yaw velocity when the ability of the tyre to transmit lateral force is exhausted, or virtually exhausted, in the extreme range, and/or the rear axle steer angle actuator (18) has failed.
 10. Device, in particular according to one of claims 5 to 9, characterized in that a disturbance estimator (66 and/or 67) is provided for at least one of the control loops provided for setting the front axle and the rear axle steer angles δ_(v) and δ_(h).
 11. Device according to claim 10, characterized in that the controller and the disturbance estimator which are assigned to the same controlled variable are designed using the same design model. 